1. Field of the Invention
The invention relates generally to a method and apparatus for sensing current in a conductor, and particularly to a method and apparatus for sensing current in a current conductor using a small, low cost current transformer.
2. Background of the Prior Art
Costs of sensing current in a conductor typically increase with increasing conductor size. Existing current sensing apparatuses typically include a current transformer that is sized according to the current expected to be seen in the conductor. Current sensors for sensing current in high current conductors, therefore, often include large expensive current transformers having a secondary current output waveform that is representative of the primary current.
Some recent attempts have been made to sense current in a conductor using small sized current transformers which are adapted to sense the primary current of the main conductor despite operating in saturation. In the current sensing apparatus described in U.S. Pat. No. 4,511,839, a circuit is adapted to provide an estimation of primary current based in part on the zero crossing point of the output waveform. Because many current transformers exhibit significant distortion in the zero crossing region, this method often results in an erroneous detection of a zero crossing, and therefore an inaccurate estimation of the primary current.
There exists a need for low cost current sensing apparatus which is adapted to accurately sense current in a conductor.